Apparatus, and associated method, for reporting a measurement summary in a radio communication system

ABSTRACT

Apparatus, and an associated method, for generating a message summary field. The message summary field indicates whether 802.11-formatted data packets are communicated upon a frequency range to which a mobile station operable in an IEEE 802.11 radio communication system is tuned. An indicator indicates whether an 802.11 data packet is detected. And, a reporter generates a measurement summary which includes a measurement summary field populated with a value indicating the determination. Subsequent analysis of the value of the field of the measurement summary is utilized pursuant to dynamic frequency selection operations.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present invention claims the priority of Application Ser. No.60/274,175, filed on Mar. 8, 2001.

The present invention relates generally to communications by acommunication station in a radio communication system operable pursuantto a first communication standard, such as the IEEE 802.11 standard, inwhich the frequency band available for use by the system is alsoutilizable by another radio communication system, operable pursuant toanother communication standard. More particularly, the present inventionrelates to apparatus, and an associated method, by which to identify, atleast in a measurement summary, whether communication activity pursuantto the first communication standard is ongoing at a portion of thefrequency band to which the communication station is tuned. Whenimplemented in a communication station operable pursuant to the IEEE802.11 standard in the 5 GHz frequency band, a measurement summary fieldis formed that indicates whether the communication station is tuned to aportion of the frequency band upon which 802.11-formatted data iscommunicated. By identifying whether the communication station is tunedto a portion of the frequency band upon which the 802.11-formatted datais communicated, subsequent retuning or communication operations at theportion of the frequency band to which the communication station istuned is effectuated.

BACKGROUND OF THE INVENTION

Advancements in communication technologies have permitted theintroduction, and popularization, of new types of communication systems.In various of such new types of communication systems, the rate of datatransmission and the corresponding amount of data permitted to becommunicated, has increased relative to existing types of communicationsystems.

New types of radio communication systems are exemplary of communicationsystems that have been made possible as a result of advancements incommunication technologies. Communication channels of a radiocommunication system are formed upon radio-links, thereby obviating theneed for conventional wire-line connections between sending andreceiving stations operable therein. A radio communication system,therefore, inherently permits increased communication mobility incontrast to conventional wire-line systems.

Bandwidth limitations sometimes limit the communication capacity of thecommunication system. That is to say, the bandwidth capacity of thecommunication channel, or channels, available to a communication systemto communicate information between sending and receiving stations issometimes limited. And, the limited capacity of the communicationchannel, or channels, limits increase of the communication capacity ofthe communication system. The communication capacity of the radiocommunication system is particularly susceptible to capacity limitationresulting from communication channel bandwidth limitations. Generally, aradio communication system is allocated a limited portion of theelectromagnetic spectrum upon which to define communication channels.Communication capacity increase of a radio communication system is,therefore, sometimes limited by such allocation. Increase of thecommunication capacity of the radio communication system, therefore, issometimes only possible if the efficiency by which the allocatedspectrum is used is increased.

Digital communication techniques provide a manner by which the bandwidthefficiency of communications in the communication system may beincreased. Because of the particular need in a radio communicationsystem to efficiently utilize the spectrum allocated in such a system,the use of digital communication techniques is particularlyadvantageously implemented therein.

When digital communication techniques are used, information that is tobe communicated is digitized. In one technique, the digitizedinformation is formatted into packets, and the packets are communicatedto effectuate the communication. Individual ones, or groups, of thepackets of data can be communicated at discrete intervals, and, oncecommunicated, can be concatenated together to recreate the informationalcontent contained therein.

Because packets of data can be communicated at the discrete intervals, acommunication channel need not be dedicated solely for the communicationof packet data generated by one sending station for communication to onereceiving station, in contrast to conventional requirements ofcircuit-switched communications. Instead, a single channel can be sharedamongst a plurality of different sending and receiving station-pairs.Because a single channel can be utilized to effectuate communications bythe plurality of pairs of communication stations, improved communicationcapacity is possible. Packet data communications are effectuated, forinstance, in conventional LANs (local area networks). Wireless networks,operable in manners analogous to wired LANs have also been developed andare utilized to communicate packets of data over a radio link, therebyto effectuate communications between a sending station and a receivingstation connected by way of the radio link.

For example, an IEEE (Institute of Electrical and Electronic Engineers)802.11 standard defines a system for operation of a wireless LAN. Thesystem is defined in terms of logical layer levels, and operationalparameters of the various layers of the system are defined in thestandard.

Proposals have been set forth to utilize an unlicensed band located at 5GHz and to implement a WLAN operable generally pursuant to the IEEE802.11 standard.

Other systems are also implementable at the 5 GHz frequency band. Aradio communication system, referred to as the HyperLan II system is,for instance, also implemented at the 5 GHz band. The HyperLan II systemis operable pursuant to a standard promulgated by the ETSI. The HyperLanII system also is a WLAN system.

As more than one communication system is operable upon common frequencyportions of the 5 GHz band, communication systems operable therein mustbe able to dynamically select the frequency band portions upon whichcommunications are effectuated. Dynamic selection is required so thatmore than one communication system does not concurrently use the samefrequencies to attempt to effectuate communications.

The European Regulatory Commission (ERC) has set forth systemrequirements of systems operable in the 5 GHz frequency band. Forinstance, amongst the requirements include a requirement that a systemoperable at the 5 GHz band generate electromagnetic energy emissionswhich are spread over available frequency channels defined therein. Thatis, the interference level formed of the communication signal energygenerated during operation of the communication system must beapproximately constant over a large bandwidth of the frequency band. Theinterference must be spread equally and must avoid interfering withcommunications in satellite and radar systems.

And, for instance, an IEEE802.11 or HyperLAN system requires that amobile station (STA) be capable of tuning to a frequency portion of thefrequency band not currently used by a basic service set (BSS). And,once tuned thereto, the mobile station is required to measure for thepresence of interference. Once the measurement is made, a report of themeasurement must be returned to an access point (AP) of the basicservice set. This procedure is referred to as dynamic frequencyselection (DFS), as a result of analysis of the measurements, an accesspoint of the basic service set determines whether to select a newfrequency range for operation of the mobile station. This procedure isreferred to as dynamic frequency selection (DFS). In a HyperLan IIsystem, mobile stations report indications of a received signal strengthindication (RSSI) block in a base band transceiver system as part of aDSF mechanism. Use of an RSSI indication, however, fails to provide anindication as to the source of interfering signals.

A manner better able to facilitate dynamic frequency selection in amobile station operable in an IEEE 802.11 system would be advantageous.

It is in light of this background information related to operation of aradio communication system in which dynamic frequency allocation isutilized that the significant improvements of the present invention haveevolved.

SUMMARY OF THE INVENTION

The present invention, accordingly, advantageously provides apparatus,and an associated method, for use in a radio communication systemoperable pursuant to a first communication standard, such as the IEEE802.11 standard, in which the frequency band available for use by thesystem is also utilizable by another communication system operablepursuant to another communication system standard.

Through operation of an embodiment of the present invention, a manner isprovided by which to identify, at least in a measurement summary,whether communication activity pursuant to the first communicationstandard is ongoing upon a portion of the frequency band to which thecommunication station is tuned. By providing the measurement summary,decisions are better able to be made regarding subsequent retuning orsubsequent communication operations of the communication station. And,thereby dynamic frequency selection is facilitated.

In one aspect of the present invention, a measurement summary field isformed by a mobile station (STA) operable pursuant, generally, to theIEEE 802.11 standard in the 5 GHz frequency band. The measurementsummary field is of a value that indicates whether the mobile station istuned to a portion of the frequency band upon which 802.11-data iscommunicated. By communicating the measurement summary field to acontrol device, such as an access point (AP) operable in the 802.11system, decisions are made regarding whether to retune the mobilestation or to commence communications upon the portion of the frequencyband at which the mobile station is tuned.

In another aspect of the present invention, the measurement summaryfield is populated with a value to indicate whether the mobile stationis tuned to a frequency range upon which 802.11 data packets arecommunicated. If 802.11 data packets are communicated at the frequencyrange to which the mobile station is tuned, the measurement summaryfield is populated with a first value. If, conversely, 802.11 datapackets are not communicated at the frequency range to which the mobilestation is tuned, the measurement summary field is of another value. Ameasurement summary including the measurement summary field iscommunicated by the mobile station to an access point at which controlfunctions are performed to control subsequent operation of the mobilestation.

In another aspect of the present invention, once the mobile station istuned to a selected frequency range, measurement is made ofcommunication energy communicated at the frequency range. Ifcommunication energy is detected, the communication energy is decoded todetect whether the communication energy forms packet-formatted data. Ifpacket formatted data is detected, further analysis of a data packet ismade to determine whether the data packet is an 802.11-formatted datapacket. Upon such detection, the measurement summary field is populatedwith a value indicating the frequency range to which the mobile stationis tuned to have 802.11-formatted data packets communicated thereon.Otherwise, an indication is populated in the measurement summary fieldto indicate that 802.11-formatted data is not communicated upon thefrequency range to which the mobile station is tuned.

In another aspect of the present invention, upon detection of thecommunication energy, and decoding thereof to detect the presence of adata packet, further analysis is made to identify whether the datapacket is an 802.11-formatted data packet or, relative to the 802.11standard, a foreign PLCP (physical layer convergence protocol)-formattedpacket. Determination of the data packet-type is made through analysisof the packet at the physical layer and logical layer above the physicallayer by which the communication system in which the mobile station isoperable. In an 802.11 system, a valid packet is determined by properdecoding of the signal field, cyclic redundancy check (CRD) on thephysical layer protocol data units (PPDU) and valid MAC address format.In contrast, a HyperLan II data packet does not have a corresponding802.11-formatted data structure. Thereby, differentiation between aHyperLan II-formatted data packet and an 802.11-formatted data packet ismade.

In one implementation, apparatus, and method, is provided for a mobilestation operable in an IEEE 802.11 WLAN. The mobile station tunes to afrequency range within the 5 GHz frequency band. Once tuned to thefrequency range, a CCA (clear channel assessment) operation isperformed. A determination is made whether the CCA indicates thefrequency range to be busy. The determination is made by detectingwhether communication energy is present on the frequencies to which themobile station is tuned. If communication energy is detected to bepresent, the mobile station further determines whether the communicationenergy forms a data packet which is formatted pursuant to the IEEE802.11 standard. To make this determination, decoding operations areperformed to detect a preamble portion of a data packet. If a preambleportion of a data packet is detected, further decoding operations areperformed upon a signal field portion of the data packet. Subsequent tosuch decoding, further inquiry of the data packet is made to check towhere the data packet is addressed. If a MAC ID (identifier) isdetected, then the data packet is a 802.11-formatted data packet. As aHyperLan II-formatted data packet does not have a corresponding 802.11formatted signal field (i.e., PLCP header) and MAC identifier, operationof an embodiment of the present invention is able to distinguish betweena HyperLan II-formatted data packet and an 802.11-formatted data packet.

In these and other aspects, therefore, apparatus, and an associatedmethod, is provided for a first radio communication system in which aselected portion of a frequency band is dynamically selectable uponwhich to communicate a first-system-type data packet. The frequency bandis also selectably utilized by a second radio communication system uponwhich selectably to communicate a second-system-type data packet.Reporting upon whether the portion of the frequency band to which acommunication station is tuned is being used to communicate thefirst-system-type data packet is performed. An indicator is at leastcoupled to receive an indication of a determination of whether thefirst-system-type data packet is communicated upon the portion of thefrequency band to which the communication station is tuned. Theindicator generates an indication signal representative of thedetermination. A reporter is coupled to receive the indication signalgenerated by the indicator. The reporter generates a report message thatincludes a field populated with a value indicative of the indicationsignal generated by the indicator.

A more complete appreciation of the present invention and the scopethereof can be obtained from the accompanying drawings which are brieflysummarized below, the detailed description of the presently preferredembodiments of the invention, and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a functional block diagram of a communication systemin which an embodiment of the present invention is operable.

FIG. 2 illustrates an exemplary format of a measurement summary framegenerated during operation of an embodiment of the present invention.

FIG. 3 illustrates the structure of a preamble portion of an IEEE802.11-formatted data packet.

FIG. 4 illustrates a functional block diagram of a delayed signalcorrelator.

FIG. 5 illustrates an exemplary relationship between a false alarm rateand a detection probability pursuant to operation of an embodiment ofthe present invention.

FIG. 6 illustrates a representation, similar to that shown in FIG. 4,but here with a different delay factor.

FIG. 7, illustrates a method at least reports whether the portion of afrequency band to which a communication station is tuned is being usedto communicate a first-system-type data packet.

DETAILED DESCRIPTION

Referring first to FIG. 1, a communication system, shown generally at10, is operable to provide packet radio communications with a mobilestation (STA) 12.

In the exemplary implementation, the communication system includes aWLAN (wireless local area network) constructed generally to be operablepursuant to the IEEE (Institute of Electrical and Electronic Engineers)802.11 standard at the 5 GHz frequency band. The mobile station 12 ishere operable, generally, pursuant to the IEEE 802.11 standard. Thecommunication system is exemplary. While operation of an embodiment ofthe present invention shall be described with respect to implementationof the communication system 10 as an IEEE 802.11 system, the teachingsof the present invention are analogously applicable in other types ofcommunication systems.

During operation of the communication system, data is communicated from,and to, the mobile station with a selected access point (AP), here anaccess point 14, of a plurality of access points, of which two accesspoints are shown in the Figure. The data is communicated by way of radiolinks 16 formed between the mobile station 12 and the selected accesspoint. Data communicated by the mobile station to the access point issometimes referred to as being communicated on a reverse link channel,and data communicated by the access point 14 to the mobile station uponthe radio link 16 is sometimes referred to as being communicated upon aforward link channel.

When data is communicated, upon either of the forward or reverse linkchannels, the data is communicated in the form of electromagneticenergy, here referred to as communication energy. In the 5 GHz frequencyband, prescribed channel allocations are not specifically allocated to aparticular communication system. That is to say, the IEEE 802.11 systemforming the communication system 10 is not specifically allocated aportion of the frequency band for its exclusive use. Instead, othersystems are also permitted to be implemented and operated at the samefrequency regions of the frequency bands. To prevent concurrent usage ofthe same frequency regions of the frequency band, dynamic frequencyselection (DFS) schemes must be utilized by devices operable incommunication systems which utilize the 5 GHz frequency band.

Generally, in a dynamic frequency selection scheme, portions of thefrequency band are dynamically selected for use upon determination thatthe frequency band regions are not being utilized for othercommunications by another communication system. If a frequency range isdetermined already to be in use, an alternate frequency range isselected upon which to effectuate communications. By providing thedynamic frequency selection, the same frequency ranges are not attemptedto be used concurrently by two, or more, separate communication systems.

As noted above, a communication system includes a plurality of accesspoints, of which two access points 14 are shown in the figures. Each ofthe access points defines a coverage area, sometimes referred to as acell. When a mobile station is positioned within a cell, communicationsof the mobile station with the infrastructure part of the communicationsystem is generally effectuated with the access point which defines thecell within which the mobile station is positioned.

The access points 14 are connected to a control hub 16. The control hubis operable to control operation of the access points and communicationsin the WLAN. The control hub, sometimes embodied at a computer server,is connected to a router that, in turn, is coupled to a packet datanetwork (PDN) 24. The packet data network is formed of, for instance,the internet backbone. And, a correspondent node (CN) 26 is coupled tothe packet data network. The correspondent node is representative of anycommunication device that is capable of communicating packet data by wayof the packet data network and, by way of a communication path formablewith the mobile station 12.

The figure further illustrates the frame structure of an IEEE802.11-formatted packet. A PLCP Preamble field 26 includes OFDM trainingsymbols. The training symbols also trigger the CCA mechanism. The PLCPPreambles of IEEE 802.11-formatted and HyperLAN II-formatted packets arenearly identical. The frame structure also includes a signal field 27.The signal field conveys modulation used in the PSDU field (describedbelow). The service field 29 includes scrambler initialization bits fordata. The PSDU field 31 forms a Physical Layer Service Data Unit fieldidentifying where the transmitted data goes. While not separately shown,a PLCP header can be used that is a combination of the signal field andthe service field.

The mobile station 12 includes a receive portion 32 operable to detect,and act upon, data communicated to the mobile station by way of aforward link channel of the radio link 16. And, the mobile stationincludes a transmit portion 34 operable to operate upon data to becommunicated upon a reverse link channel of the radio link 16 to theaccess point.

The mobile station also includes apparatus 38 of an embodiment of thepresent invention. The apparatus is operable, pursuant to dynamicfrequency selection operations of the mobile station and network portionparts of the communication system, to permit communication operations tobe performed by the mobile station at a frequency range to which themobile station is tuned or, alternately, to instruct the mobile stationto tune to another frequency range. The apparatus is coupled to both thereceiving and transmit portions of the mobile station.

The elements of the apparatus 38 are functionally represented.Implementation of the elements of the apparatus is made any desiredmanner. In the exemplary implementation, the elements form, at least inpart, algorithms executable by suitable processing circuitry. Once themobile station is tuned to a selected frequency range, circuitry of thereceive portion detects communication energy on the forward linkchannels of the radio link within the frequency range to which themobile station is tuned. Indications of the detected communicationenergy, or lack thereof, are provided by way of the line 42 to anindicator 44 of the apparatus 38.

The indicator 44 includes an activity determiner 46. The activitydeterminer here performs a clear channel assessment (CCA) operation. Theclear channel assessment operation determines whether communicationenergy is present upon the frequency range to which the mobile stationis tuned. The activity detector is coupled to a decoder 48. And, thedecoder is also coupled by way of the line 42 to receive indications ofcommunication energy, if any, received by the receive portion of themobile station. The decoder is operable, upon detection of communicationenergy by the activity detector to attempt to decode the communicationenergy.

And, the indicator 44 also includes a packet address detector. Thepacket address detector is also coupled to the line 42 to receiveindications of communication energy, if any, received at the receiveportion of the mobile station. The packet address detector is operablewhen the decoder detects the presence of a data packet, such as bydetecting a part of the preamble portion of a data packet which isformed at a physical (PHY) logical layer of the 802.11 communicationsystem. The packet address detector 52 detects whether an MAC (mediumaccess control) layer packet address is part of the receivedcommunication energy. A HyperLan-lI-formatted data packet does notinclude 802.11 formatted signal field and MAC-layer packet address. Thepacket address detector thereby is able to distinguish between aHyperLan-II-formatted data packet and an 802.11-formatted data packet.

The apparatus 38 further includes a reporter 56 that is coupled to thepacket address detector 52 of the indicator 44. The reporter 56 isoperable to generate a measurement summary that includes a fieldpopulated with a value indicating whether the frequency range to whichthe mobile station is tuned contains an 802.11-formatted data packet. Ifanother data packet-type data packet is detected, such as aHyperLan-II-formatted data packet, the field is populated with anothervalue. The field thereby at least indicates whether a frequency range towhich the mobile station is tuned is being used to communicate an802.11-formatted data packet or a data packet formatted pursuant to aforeign PLCP (physical layer convergence protocol).

The measurement summary is provided to the transmit portion 34 by way ofthe line 58.

The transmit portion transmits the measurement summary by way of areverse link channel formed upon the radio link 16 back to the accesspoint. Here, once received at the access point, indications of themeasurement summary are routed to the control hub 18, or otherappropriate structure. Analysis of the measurement summary is made atthe control hub, and the control hub selects whether the mobile stationshould remain tuned to the frequency range or become retuned to anotherfrequency range.

FIG. 2 illustrates an exemplary measurement summary, shown generally at68, formed by the apparatus 38 of the mobile station shown in FIG. 1.The measurement summary includes a plurality of fields, including afield 72. The field 72 is a single-bit field, here identified as aforeign PLCP header field. The field is populated with a first valuewhen a PLCP is detected upon the frequency range to which the mobilestation is tuned during a measurement interval, but, if no valid signalfield is subsequently detected, such as that which occurs when aHyperLan-II-formatted data packet is communicated upon a communicationchannel defined within the frequency range to which the mobile stationis tuned. And, the field 72 is of another value when an 802.11-formatteddata packet is detected.

The measurement summary 68 here also includes additional single-bitfields 74, 76, 78, 82, 84, 86, and 88. The field 74 is a BSS (basicservice set) field, the value of which specifies whether at least onevalid MAC header was decoded for the measured frequency channel. Thefield 76 is a QBSS field. The value of the field 76 specifies whetherthe at least one BSS is running in QBSS. The bit is set only if themobile station is IEEE 802.11(e) MAC enabled. Fields 82 and 84 arevalues indicating whether the to DS field and from DS field is setduring the frame during which the measurement is made by the mobilestation.

The field 84 is a periodicity field. The periodicity field is of a valuewhich specifies whether at least two consecutive CCA (clear channelassessment) measurements of busy and on/off patterns are periodic. Asignal is classified as periodic if at least two consecutive CCA busyduration and CCA busy intervals are identical. The field 86 is anextended CCA report field. The value of the field 86 specifies whetherthe CCA busy fraction, CCA busy duration, and CCA busy interval arepresent in the report. And, the field 88 is an extended BSS report. Thevalue of the field 88 specifies whether the measurement report framecontains a detailed report.

Turning next to FIG. 3, to provide a basic understanding of what ClearChannel Assessment (CCA) is, below is a description of the IEEE802.11apreamble and how the preamble is used in CCA. In addition, simulationsshow that a system with a Physical Layer (PHY) similar to IEEE802.11acan trigger the CCA mechanism even at very low SNRs. Thus, it isimportant to detect the presence of systems that use a PHY similar toIEEE802.11a, but have a different Media Access Control (MAC) and reportthis during a Dynamic Frequency Selection (DFS) measurement.

The preamble shown in FIG. 3 is pre-appended to all data bursts in aIEEE802.11a WLAN system where “B” represents a short training symbol ofwhich the first short training symbol 101 is an example. The shortsymbols produce a waveform with a periodicity of 0.8 us. The shortsymbols are the first part of the packet received by the radio frequency(RF) in the orthogonal frequency division multiplexing (OFDM)demodulator; thus, the first two symbols may be distorted due tosettling of the gain control loop and the associated quantizationeffects. However, the remaining eight short symbols provide ample energyfor reliable packet detection and clear channel assessment. The key isin having sufficient averaging to reduce the effects of additive noise.

The long symbols 105 are shown in FIG. 1 as “C” where the long symbolsand short symbols are separated using a cyclic prefix 121 indicated asCP. The CP 121 allows for a channel estimation of the long symbols 105without the influence of Intersymbol Interference ISI. The long symbols105 are 3.2 us in duration, excite all frequencies in the occupied bandand provide sufficient samples for channel estimation.

The Delay Correlation Method

The principle of delay and correlate method is to correlate the receivedsignal with a delayed version of itself. The idea is to exploit theparticular structure of the preamble in order to obtain reliableestimates of start of a data burst. A block diagram of the basicstructure is shown in FIG. 4. If the input signal consists of complexsamples r(i), the correlator has a delay D and a moving average windowsize of L then the correlator output can be written:

${.\;{P(k)}} = {\sum\limits_{n = 0}^{L - 1}\;{{r^{*}\left( {k + n} \right)} \cdot {r\left( {k + n + D} \right)}}}$

Considering a received signal model of r(k)=s(k)exp(j2π/₀t)+n(k), then

${P(k)} = {{\sum\limits_{n = 0}^{L - 1}{{{s\left( {k + n} \right)}}^{2}{\exp\left( {{j2}\;\pi\; f_{0}D} \right)}}} + {{n^{*}\left( {k + n} \right)}{n\left( {k + n + D} \right)}}}$where s(k+n+D)=s(k+n)exp(j2π/₀D) assuming that s(k) are samples from theshort training symbols with a periodicity of modulo D. Examining P(k)from above, a maximum is achieved when k=D+L.

A critical function for the IEEE802.11 MAC carrier sense, multipleaccess protocol is obtaining a clear channel assessment (CCA). CCA isused by a station (STA) to determine if the channel is clear and anaccess attempt is possible. The IEEE802.11a WLAN specification requiresthat the received signal levels equal or greater to the minimumsensitivity for BPSK (−82 dBm) will cause CCA to indicate “Busy” to theMAC when a preamble is detected. The probability of detection, i.e., theprobability that CCA algorithm will correctly identify a busy condition,is P_(D)>90% (as defined in IEEE802.11a WLAN Specification).

CCA can be considered a binary hypothesis test to determine if themedium is busy. It consists of the hypothesis H₁ which indicates thatthe channel is busy and the hypothesis H₀

which indicates that the channel is idle. The test statistic is definedas

$\begin{matrix}{S = {{\sum\limits_{k = 1}^{N}\;{{P(k)}}^{2}} \geq {T\; h}}} & (6.1)\end{matrix}$under hypothesis H₁, and

$\begin{matrix}{S = {{\sum\limits_{k = 1}^{N}\;{{P(k)}}^{2}} < {T\; h}}} & (6.2)\end{matrix}$under hypothesis H₀, where Th is the threshold, and N is the number ofredundant measurements.

When there is no preamble, the magnitude of S decreases generally withsignal to noise ratio (SNR). However, the kurtosis, defined by

$\sum\limits_{i}\frac{\left( \;{{{P(i)}}^{2} - \overset{\_}{S}} \right)^{4}}{{N\left( {\hat{\sigma}}^{2} \right)}^{2}}$increases. Here {circumflex over (σ)}² is an estimated variance and{overscore (S)} is the sample mean.Simulation results are described here.

To show the output of the CCA algorithm when a either IEEE802.11a orHiperLAN II PHY is detected, simulation results are presented with thefollowing assumptions:

-   (1) Packet size: 512-bit,-   (2) Rate: R=¾, with puncturing and interleaving,-   (3) The generator polynomials for the convolutional coding:    V₁(D)=(1+D²+D³+D⁵+D⁶) and V₂(D)=(1+D+D²+D³+D⁶), with K=7, and    d_(free)=10,-   (4) 64-QAM for a modulation,-   (5) Channel: 5-tap Rayleigh channel with taps {0.749, 0.502, 0.3365,    0.2256, and 0.1512}.

It should be pointed out that the choice of modulation will have noimpact on CCA when the preamble is detected. 64 QAM is chosen as themodulation type when the preamble is not used in determining channelstate due to the SNR range being approximately 20 dB above the minimumsensitivity for BPSK.

In the simulations, we considered two scenarios, (a) with preamblesymbols, and (b) no preamble symbols.

The first scenario includes using preamble symbols: The delay factorused in the computation of the correlation outputs is 16 (i.e., distancebetween short symbols) and Monte-Carlo simulation methodology was usedto estimate performance. FIG. 4 is the probability detection 301 and303, P_(D), and the false-alarm rate 321, P_(F), where the probabilitydetection 301 and 303 P_(D) grows with increasing SNR. For example, theP_(D) for SNR=20 is shown as a first function. In addition, this figureindicates a reliable false-alarm rate, P_(F)<<0.1 at P_(D)≈0.9.

The second scenario operates without using preamble symbols: For thesame simulation conditions as in the first scenario, FIG. 5 shows P_(D)and P_(F) for different SNRs. A delay factor of 64 is chosen due to thedistance between the cylix prefix and the beginning of an OFDM symbol.FIG. 5 indicates that P_(D) decreases generally with SNR which matchesthe result in FIG. 4. We can also keep P_(F)<<0.1 at P_(D)≈0.9. As inthe first scenario, the Monte-Carlo simulation technique is used to findP_(D) 401, 403 and 405.

While CCA was designed as a means to allow Stations in an IEEE802.11aWLAN system to assess if the channel was clear for transmission, CCA canalso be used when doing a DFS measurement to determine the existence ofPHYs that are similar to IEEE802.11a. In fact, as the simulation resultsshow, this can be done at SNRs approaching 0 dB. Thus, the inventionproposes that the following steps be taken when performing a measurementfor the purposes of DFS.

-   -   1. The STA tunes to a desired frequency to do a measurement.    -   2. The STA using the energy measurement feature of the        IEEE802.11a tranceiver measures the received signal strength        (prior art).    -   3. The STA examines the output of the CCA hypothesis test.    -   4. If CCA triggers true, the STA listens for a Beacon Frame from        an IEEE802.11a WLAN system.    -   5. If the STA cannot identify a valid IEEE802.11a Beacon Frame,        then it determines that there is a PHY similar to IEEE802.11a,        but the MAC is foreign.    -   6. The STA reports to the AP that a PHY similar to IEEE802.11a        was found, but the MAC was foreign.

The frame used to send measurement data to the AP could be as shown inFIG. 6, which includes Frame Control (501), Duration 503, DA 505, SA507, BSSID 509, Sequence Control 511, RSSI 513, CCA true MAC foreign yesor no 515 and FCS 517.

Table 2 shows the frequency allocation for WLAN operation in Europe andhow the frequencies are allotted for HiperLAN II.

TABLE 2 Center Frequencies Effective (20 MHz Spacing) Radiated Power5180–5320 23 dBm 5500–5680 30 dBm 5700 23 dBm

FIG. 7 illustrates a method, shown generally at 550, of an embodiment ofthe present invention. The method at least reports whether the portionof a frequency band to which a communication station is tuned is beingused to communicate a first-system-type data packet. The communicationstation is operable in a first radio communication system in which aselected portion of a frequency band is dynamically selectable uponwhich to communicate a first-system-type data packet. The frequency bandis also selectably utilized by a second radio communication system uponwhich to selectably communicate a second-system-type data packet.

First, and as indicated by the block 552, an indication signalrepresentative of a determination of whether the first-system-datapacket is communicated upon the portion of the frequency band to whichthe communication station is tuned is generated. Then, and as indicatedby the block 554, a report message is formed. The report messageincludes a field populated with a value indicative of the indicationsignal.

Thereby, a report message is formed that indicates whether communicationactivity pursuant to a first radio communication system is ongoing at aportion of the frequency band to which the communication station istuned. Upon analysis of the report message, subsequent retuning, orsubsequent communication, operations are caused to be performed by thecommunication station.

The preferred descriptions are of the preferred examples forimplementing the invention, and the scope of the invention should notnecessarily be limited by this description. The scope of the presentinvention is defined by the following claims.

1. A method for changing the channel assignment in a wireless LAN systemusing a clear channel assignment mechanism for randomly accessing achannel, said method comprising the steps of: tuning to the desiredfrequency; performing a Clear Channel Assessment test; determining abeacon deacon decodability; and if a valid IEEE (Institute of Electricaland Electronic Engineers) 802.11a Beacon Frame cannot be identified,reporting to an access point that a physical layer similar toIEEE802.11a was found, but that a found media access control wasforeign.
 2. In a wireless local area network in which a selected portionof a frequency band is dynamically selectable upon which to communicatea first-system-type data packet, the frequency band also selectablyutilized by a second radio communication system upon which selectably tocommunicate a second-system-type data packet, an improvement ofapparatus for a communication station operable in the wireless localarea network, said apparatus at least for reporting whether the portionof the frequency band to which the communication station is tuned isbeing used to communicate the first-system-type data packet, saidapparatus comprising: an indicator at least coupled to receive anindication of a determination of whether the first-system-type datapacket is communicated upon the portion of the frequency band to whichthe communication station is tuned, said indicator for generating anindication signal representative of the determination; and a reportercoupled to receive the indication signal generated by said indicator,said reporter for generating a report message that includes a fieldpopulated with a value indicative of the indication signal generated bysaid indicator.
 3. The apparatus of claim 2 wherein the communicationstation comprises a receive portion and wherein said indicator comprisesan activity determiner coupled to the receive portion; said activitydeterminer for determining activity upon the selected portion of thefrequency band to which the communication station is tuned, saidactivity determiner for indicating at least when communication energy isdetermined to be present upon the selected portion of the frequencyband.
 4. The apparatus of claim 3 in which the communication system isoperable pursuant to an operational protocol which defines a clearchannel assessment operation and wherein said activity determinerperforms a clear channel assessment operation.
 5. The apparatus of claim4 wherein said indicator further comprises a decoder coupled to saidactivity determiner and coupled to receive indications of thecommunication energy when determined to be present upon the selectedportion of the frequency band, said decoder for decoding at least partof the communication energy to determine whether the communicationenergy comprises at least one of the first-system-type data packet andthe second-system-type data packet.
 6. The apparatus of claim 5 whereinthe first-system-type data packet is defined in terms of logical layersincluding a physical (PHY) layer and at least one higher-level layer,and wherein said identifier further comprises a packet address detectoroperable responsive to determination by said decoder that thecommunication energy comprises at least one of the first-system-type andsecond-system-type data packets, respectively, said packet addressdetector for detecting whether the at least one of the first-system-typeand second-system-type data packets further comprises a packet addressin the higher-level layer.
 7. The apparatus of claim 6 wherein thefirst-system-type data packet is formatted according to a selectedhigher-level layer protocol and wherein said packet address detectordetects when the communication energy comprises the data packetformatted according to the selected higher-level layer protocol.
 8. Theapparatus of claim 7 wherein the wireless local area network is operablepursuant to an IEEE (Institute of Electrical and Electronic Engineers)802.11 standard and wherein said packet detector detects when thecommunication energy comprises an IEEE 802.11-formatted data packet. 9.The apparatus of claim 2 wherein the field of the report messagegenerated by said reporter is formed of a first digital value when theindication signal is of a first value and is formed of another digitalvalue when the indication signal is other than the first value.
 10. Theapparatus of claim 2 wherein the wireless local area network is operablepursuant to an IEEE (Institute of Electrical and Electronic Engineers)802.11 standard and wherein the field of the report message generated bysaid reporter is of a value indicative of whether an802.11-standard-formatted data packet is determined to be communicatedupon the portion of the frequency band to which the communicationstation is tuned.
 11. The apparatus of claim 10 wherein thesecond-system-type data packet is formatted pursuant to a foreign,relative to the IEEE 802.11 standard, PLCP (physical layer convergenceprotocol) and wherein said indicator distinguishes between the802.11-standard-formatted data packet on a foreign-PLCP-formatted datapacket forming the second-system-type data packet.
 12. The apparatus ofclaim 11 wherein said reporter generates a communication-stationmeasurement summary and wherein the field populated with the valueindicative of the indication signal generated by said indicatorcomprises a portion of the communication-station measurement summary.13. In a method for communicating in a wireless local area network inwhich a selected portion of a frequency band is dynamically selectableupon which to communicate a first-system-type data packet, the frequencyband also selectably utilized by a second radio communication systemupon which selectably to communicate a second-system-type data packet,an improvement of a method for a communication station operable in thewireless local area network, said method at least for reporting whetherthe portion of the frequency band to which the communication station istuned is being used to communicate the first-system-type data packet,said method comprising: generating an indication signal representativeof a determination of whether the first-system-type data packet iscommunicated upon the portion of the frequency band to which thecommunication station is tuned; and forming a report message thatincludes a field populated with a value indicative of the indicationsignal generated during said operation of generating.
 14. The method ofclaim 13 comprising the additional operation, prior to said operation ofgenerating, of determining activity upon the selected portion of thefrequency band to which the communication station is tuned, the activityupon the selected portion of the frequency band indicated at least whencommunication energy is determined to be present upon the selectedportion of the frequency band.
 15. The method of claim 14 wherein thecommunication system is operable pursuant to an operational protocolwhich defines a clear channel assessment operation, and wherein saidoperation of determining comprises performing a clear channel assessmentoperation.
 16. The method of claim 15 further comprising the operation,subsequent to said operation of performing, of decoding at least part ofthe communication energy, when determined during said operation ofdetermining to be present, to determine whether the communication energycomprises at least one of the first-system-type data packet and thesecond-system-type data packet.
 17. The method of claim 16 wherein thefirst-system-type data packet is defined in terms of logical layersincluding a PHY (physical) layer and at least one higher-level layer,and wherein said method further comprises the operation of detectingwhether the at least one of the first-system-type and second-system-typedata packets, respectively, further comprises a packet address in thehigher-level layer.
 18. The method of claim 17 wherein the wirelesslocal area network is operable pursuant to an IEEE (Institute ofElectrical and Electronic Engineers) 802.11 standard and wherein saidoperation of detecting comprises detecting when the communication energycomprises an IEEE 802.11-formatted data packet.
 19. The method of claim13 wherein the wireless local area network is operable pursuant to anIEEE (Institute of Electrical and Electronics Engineers) 802.11 standardand wherein the field of the report message generated during saidoperation of generating is of a value indicative of whether an802.11-standard-formatted data packet is determined to be communicatedupon the portion of the frequency band to which the communicationstation is tuned.
 20. In a communication station operable in a wirelesslocal area network that operates pursuant to an IEEE (Institute ofElectrical and Electronics Engineers) 802.11 standard within a frequencyband also used by another communication system, an improvement ofmeasurement summary apparatus at the communication station, saidmeasurement summary apparatus comprising: a selected field populator forpopulating a selected field of a measurement summary with an indicationof whether a portion of the frequency band to which the communicationstation is tuned is being used to communicate an802.11-standard-formatted data packet, the indication comprising a firstvalue if the portion of the frequency band is being used to communicatean 802.11-standard-formatted data packet, and a different value if theportion of the frequency band is being used to communicate a data packetother than an 802.11-standard-formatted data packet.